PECAM1 and neoplasm: VEGF is a dimeric glycoprotein that is a highly specific mitogen for vascular endothelial cells in vitro, as well as inducing migration and preventing apoptosis of these cells in vivo; VEGF expression by tumor cells is stimulated by hypoxia, paracrine cytokines and activated oncogenes and it provides a wide surface of permeable CD31-positive microvessels from which tumor cells can be sustained and enter the circulation [4,14,16,17].